EmonTX keeps disconnecting from EmonBase

Yes, but you are using a different method of connection between the emonTx and your emonBase. The emonTx is SENDING different information in each case. Specifically, the radio sends all the data every time so that the names can be matched at the receiving end; the serial connection (because the variable name is attached to each data item) doesn’t need to send everything, it only sends the things that are in use.

When the message was sent by radio, it was tagged with the Node ID “15” at source in the emonTx. EmonHub translated that into “emontx3cm15”. Now that you’re receiving it directly into the RPi, it’s coming in via a different route minus the NodeID. You need to edit your interfacer (via the web browser and emonHub) according to this post: EmonTX to Rpi - Direct Serial Connection - #49 by borpin
If you want to continue to call it Node 15, you must delete that node definition lower down the file in the [nodes] section.

Before you delete Node 15, look at it - that’s where the names get attached to the values that come in by radio.